Same Building, Two Conventions, Opposite Answers

1. A citation to a chapter that does not exist

This article began with a line I saw in a bibliography:

The code does have a Chapter 16 — but on a different subject: the design of foundation soils and foundations under earthquake effects. A chapter containing special provisions for historic structures does not exist in it.

2. How often does the code mention historic structures?

In the full official text the word "historical" appears three times:

1. Clause 1.1.8 — placing registered structures outside the scope.
2. Clause 15.1.5 — repeating the same exclusion for the existing-buildings chapter.
3. Once more in the phrase "the date of the document" — an entirely different sense of the Turkish word.

So both genuine occurrences exist in order to exclude such structures. The code contains no calculation rule, factor or performance criterion for them.

3. Two separate capacity conventions

In TAR-01 we saw that for an out-of-scope structure the fallback clause opens a route. But in following that route you must choose something: by which convention will the capacity be computed?

The new-design convention

When designing a new building the characteristic strength is divided by a partial material factor. For masonry the code gives it explicitly: 1.75 for autoclaved aerated concrete, 2.0 for other materials.

The existing-building assessment convention

When assessing an existing building the logic changes. In new design the material has not yet been produced and the uncertainty points forward. In an existing building the material is there and can be measured; the uncertainty is about how well you measured it.

4. The clause that gets skipped

The clause is unambiguous: in assessing an existing building you do not divide by γ_m. Instead the knowledge level factor is applied:

The two conventions run in opposite directions: one divides, the other multiplies. Confusing them changes the capacity by more than a factor of two.

5. Numerical comparison

We use the same data as TAR-01: twenty-six piers of a registered school building, shear governing. The calculation in that article followed the new-design convention and used an effective divisor of 2.222 (γ_m = 2.0 together with an additional 0.9 effective area factor).

6. The verdict flips

This is not a rounding difference or a detail. About the same building, one calculation says "fourteen walls lack capacity, strengthening is required" while the other says "every wall is adequate". Both come from the same measurements, the same model and the same code relations.

6b. This very data set mixes the two conventions

The discussion so far has been about principle. But looking at the calculation this article rests on, one finds that the thing described is exactly what was done there.

The header of the source calculation table reads: κ = 0.90 | γ_M = 2.0. That is, the capacity is both divided by the material factor and multiplied by the knowledge level factor:

6c. The second invisible choice: f_vk0

The capacity convention is not the only invisible choice. For the same building, two separate documents use two different initial shear strengths: 0.20 MPa and 0.125 MPa. Everything else — demands, geometry, κ, γ_M — is identical.

TBDY Table 11.3 gives three values for brick masonry: 0.30 with M10–M20 mortar, 0.20 with M2.5–M9, and 0.10 with M1–M2. This building is laid in lime mortar. The compressive strength of historic lime mortar is typically below 1 MPa — that is, below even M1.

7. So which one is right?

The uncomfortable answer is this: for this building, formally, neither.

• Clause 15.2.12(b) and the knowledge level table belong to the existing-buildings chapter. Clause 15.1.5 places registered structures outside that chapter. So the knowledge level factor is not binding on this building.
• The γ_m value belongs to the design of new masonry buildings. Applying it directly to an existing, registered structure is also an interpretation.

We are not declaring either side correct. What we are saying is narrower and firmer: the choice has a factor of 1.67 attached to it and it reverses the verdict; a choice of that size cannot remain invisible.

In practice the more conservative route is a defensible route — material uncertainty in a historic structure exceeds that in a modern building. But that caution must be declared with its reason, not buried inside a divisor.

8. Why knowledge level is decisive here

The logic of the knowledge level factor is this: what reduces the capacity is not the weakness of the material but how well you know it. Limited knowledge gives 0.75, comprehensive knowledge 1.00.

In a historic structure that logic weighs even more heavily, because the sources of uncertainty multiply:

• Section uncertainty. A historic wall is usually layered: two dressed faces with rubble infill between. The thickness measured from outside may not represent the load-bearing section.
• Mortar uncertainty. The initial term of the shear strength, f_vk0, comes directly from mortar bond, and the mortar has changed over centuries.
• Past interventions. Previous repairs are undocumented; different materials may have been used in different periods.
• Sampling limits. In a registered structure the number and location of cores are restricted — precisely when you want to raise the knowledge level, you may not intervene.

9. Material uncertainty and test methods

Method selection is governed by the trade-off between knowledge level and damage to the fabric:

That last row connects directly to this series. In TAR-01 we saw f_vk = f_vk0 + 0.4σ_d: the shear strength depends on the vertical stress. A flat-jack makes it possible to measure σ_d rather than estimate it from a model — removing one of the largest items of model uncertainty outright.

10. What must the report say?

In TAR-01 we saw how the scope declaration should be written. The capacity convention must be added to it:

Long. But every sentence carries a decision and the magnitude of that decision. The shortened version — "capacities were computed in accordance with the Code" — tells the reader nothing and cannot be audited.

11. Test yourself

1. What is the subject of the code's Chapter 16? Where are the special provisions for historic structures?
2. What does Clause 15.2.12(b) say, and in which direction does it depart from the new-design convention?
3. Does the knowledge level factor multiply or divide the capacity? If the two conventions are mixed, in which direction is the error?
4. Is the knowledge level factor binding on a registered structure? Why?
5. What quantity does a flat-jack measure, and how does it enter the shear strength?
6. What is the paradox in raising the knowledge level of a historic structure?
7. Why is "capacities were computed in accordance with the Code" inadequate?